Methods and systems for improved detection of minispare tires

ABSTRACT

A method of detecting a minispare tire in a vehicle having a vehicle control system. The method includes detecting a rotational velocity of each of a plurality of wheels of the vehicle; determining whether a minispare tire is mounted on the vehicle based on the rotational velocities detected at each of the plurality of wheels; adjusting the vehicle control system if a minispare tire is mounted on the vehicle; sensing a hydraulic pressure of a braking system of the vehicle; and suspending determination of whether a minispare tire is mounted on the vehicle if the hydraulic pressure exceeds a predetermined critical pressure level.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/211,258 filed September 16, 2008, the entire content of which ishereby incorporated by reference.

BACKGROUND

The present invention relates to vehicle control systems, and inparticular to methods and systems for detecting the presence of aminispare tire and suspending detection during braking.

Minispare tires are an alternative to full-sized spare tires invehicles. The minispare tire is typically smaller, weighs less, and hasa higher inflation pressure than a regular tire and, when installed inplace of a damaged conventional tire, is sufficiently durable to allowthe vehicle to travel to a nearby service station for assistance.

While minispares have a number of positive attributes, their smallerdimensions and higher inflation pressure compared to standard tires, canalter the performance of a vehicle's electronic stability control (ESC)system, traction control system (TCS), or antilock braking system (ABS).Therefore, vehicles include sensors or other devices to detect thepresence of a minispare tire, so that appropriate corrections to thevehicle controls can be made to account for the presence of theminispare tire. Detection of a minispare tire is performed on acontinuous basis, for example, by measuring the relative speeds of thewheels on the vehicle. Due to the smaller circumference, a minisparetire will have a greater rotational velocity than standard-sized tiresat a given vehicle speed. Thus, if one wheel has a significantly higherrotational velocity than the others, it is assumed that a minispare tireis present and appropriate corrections are made in the vehicle controlsystems (e.g., ESC, TCS, and ABS).

However, detection of minispare tires is temporarily suspended when thevehicle's brakes are applied, in part because one or more tiresincluding the minispare could slip during braking, which could lead toincreased detection times or possibly inaccurate wheel-speedmeasurements. This is a particular problem on surfaces with a lowcoefficient of friction (low-p surfaces) such as ice or wet pavement.

One method that has been used to detect whether the vehicle's brakes arebeing applied is to determine whether the brake light switch (BLS) hasbeen activated. The BLS is directly coupled to the brake pedal itselfand responds to minimal movement of the pedal, even before any hydraulicpressure is built up in the braking system. When the BLS is activatedthe vehicle's control systems suspend minispare detection.

SUMMARY OF THE INVENTION

A problem may arise with suspending minispare detection based on BLSactivation when the vehicle is driven by a so-called ‘two-footed’driver. Drivers who control the accelerator and brake pedals using bothfeet, with one foot continuously resting on the brake pedal, apply asmall amount of pressure to the brake pedal, which activates the BLSand, as a consequence, suspends minispare detection. For a two-footeddriver who routinely leaves a foot resting on the brake pedal, thismeans that minispare detection is suspended for a significant amount oftime that the vehicle is in operation.

In one aspect, the invention provides a method of detecting a minisparetire in a vehicle having a vehicle control system. The method includesdetecting a rotational velocity of each of a plurality of wheels of thevehicle; determining whether a minispare tire is mounted on the vehiclebased on the rotational velocities detected at each of the plurality ofwheels; adjusting the vehicle control system if a minispare tire ismounted on the vehicle; sensing a hydraulic pressure of a braking systemof the vehicle; and suspending determination of whether a minispare tireis mounted on the vehicle if the hydraulic pressure exceeds apredetermined critical pressure level.

In another aspect, the invention provides a system for suspendingdetection of a minispare tire in a vehicle. The system includes aplurality of wheel speed sensors, where each speed sensor is attached toa wheel of the vehicle such that the speed sensor measures a rotationalvelocity of the wheel. The system also includes a braking systemincluding a master cylinder; a brake pedal attached to the mastercylinder; and a hydraulic pressure sensor to measure hydraulic pressurewithin the braking system. The system further includes a vehicle controlsystem having a control unit in operative communication with the brakingsystem and wheel speed sensors. The control unit has a logic unit and astorage unit. The storage unit has a “critical pressure level” valuestored therein. The logic unit is configured to receive the rotationalvelocity values from the wheel speed sensors; analyze the relativerotational velocities of the wheels to determine whether a minisparetire is mounted on a wheel; receive the hydraulic pressure value fromthe hydraulic pressure sensor; compare the hydraulic pressure value tothe critical pressure level stored in the storage unit; and, if thehydraulic pressure level is less than or equal to the critical pressurelevel, adjust the vehicle control system for the presence of a minisparetire.

In still another aspect, the invention provides a method of operating avehicle control system. The method includes detecting a rotationalvelocity of each of a plurality of wheels of a vehicle; sensinghydraulic pressure in a braking system of the vehicle; determiningwhether a minispare tire is mounted on the vehicle based on therotational velocities of the wheel, if the hydraulic pressure in thebraking system is at or below a predetermined critical pressure; andadjusting the vehicle control system if it has been determined that aminispare tire is mounted on the vehicle.

In yet another aspect, the invention is a method of detecting atwo-footed driver in a vehicle. The method includes driving a vehicle ata constant speed; increasing pressure applied to a braking system of thevehicle; measuring hydraulic pressure in the braking system; andrecording a critical hydraulic pressure in the braking system when thevehicle speed deceases.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which:

FIG. 1 is a graph showing the relation between ‘deceleration threshold’and ‘wheel brake pressure’ for a light load or a heavy load; and

FIG. 2 is a diagram of the elements of a braking system for a vehiclehaving an antilock braking system (ABS).

DETAILED DESCRIPTION OF THE INVENTION

Before any constructions of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other constructions and of being practicedor of being carried out in various ways.

An improved system and method of detecting minispare tires involvesdetecting the braking pressure applied by the driver and suspendingminispare tire detection only when braking pressure exceeds apredetermined critical level, i.e., a level at which braking pressurethat is applied at the wheels could lead to inaccurate wheel speedmeasurements.

Typically, a two-footed driver will adjust the level of pressure that heor she applies to the brake pedal so as not to produce noticeableslowing of the vehicle. At or below this minimal level of applied brakepressure, minispare detection can be conducted without a concern thatthe wheels will slip due to braking or that detection times will beincreased, as might happen during heavier braking.

FIG. 1 shows the relation between ‘deceleration threshold’ and ‘wheelbrake pressure’ for different types of load. The wheel brake pressure isthe hydraulic pressure generated at the wheel. The decelerationthreshold is the value of the hydraulic pressure generated at the wheelwhich would lead to deceleration of the vehicle. In one construction,the deceleration threshold is the hydraulic pressure which leads to atleast a 5 kilometers per hour (kph) decrease in vehicle speed. Ingeneral, the deceleration threshold is a function of gross vehicleweight (GVW) and the coefficient of friction between the tires and thesurface on which the vehicle is traveling. Thus, in one construction theinvention involves identifying a critical pressure level of thehydraulic braking system at which noticeable deceleration of the vehicleoccurs. This critical pressure level is also related to how tightly thebrake mechanisms (the calipers or shoes) grip the wheels (via the discsor drums), which in turn can depend on the age and condition of thecomponents of the braking system.

To implement the present methods in a vehicle control system, a criticalhydraulic braking pressure level is determined for a particular vehicleor class of vehicles, as discussed further below. In practice, setting acritical hydraulic braking pressure level in a vehicle control systemmay take into account either the typical or the upper limit of GVW forthe vehicle, as well as either the typical or the lower limit ofcoefficient of friction for the surfaces that the vehicle is expected toencounter.

After determining the critical hydraulic braking pressure level, thisinformation is programmed into the controller for the vehicle controlsystem(s). The controller for the particular vehicle control systemgenerally includes a logic unit and data storage unit and receivesinputs from various sensors which can include wheel speed sensors and abrake hydraulic pressure sensor. The controller is programmed todetermine rotational velocities of each of the wheels, and to determinethe presence of a minispare tire, unless brake pressure above thecritical level is applied. The critical hydraulic braking pressure levelis entered into the data storage unit. The data storage unit may containa single pressure level which corresponds to the critical hydraulicbraking pressure level for the particular vehicle that the controller isassociated with. Alternatively, a table of critical hydraulic brakingpressure levels may be entered into the data storage unit, the valuescorresponding to critical pressure levels for several different vehiclesin which the controller may be installed. Upon installation into aparticular vehicle, the controller is programmed to use the criticalpressure value associated with that vehicle.

The described methods can be used on various types of vehicle controlsystems which monitor wheel speed and which are affected by the presenceof a minispare tire, including an antilock braking system (ABS) and atraction control system, which may be parts of a comprehensiveelectronic stability control (ESC) system.

In various constructions, the brake pressure (e.g., measured in themaster cylinder, or alternatively in other parts of the braking system)at which minispare detection is suspended can be determined in a roadtest. In one test, a vehicle was driven by a two-footed driver at aconstant speed of 50 kph. While applying a constant throttle to maintainspeed, the driver gradually depressed the brake pedal until the vehiclebegan decelerating noticeably, which corresponded to a 5-10 kph decreasein vehicle speed. Hydraulic brake pressure levels in the master cylinderwere measured and the level of pressure at which no noticeable slowingof the vehicle was used as the threshold for minispare detection. In onetest in which the vehicle was a sport-utility vehicle (SUV), it wasdetermined that noticeable slowing of the vehicle did not occur untilthe brake master cylinder pressures exceeded 10 bar. Therefore minisparedetection could be conducted up to that pressure level, and at hydraulicpressures above this level minispare detection would be suspended. Theabove pressure values pertain to braking on high friction surfaces(e.g., dry asphalt, dry concrete, and the like). However, in variousconstructions the pressure values will differ based on the roadconditions, e.g. whether the road surfaces are wet or icy, as well asthe type and condition of the brakes and the total weight of thevehicle.

Other braking tests were performed in a controlled setting with brakingpressure applied automatically. Table 1 shows exemplary brake hydraulicpressures, determined in a controlled setting, above which minisparedetection is suspended.

TABLE 1 Brake hydraulic pressure leading to reduction in vehicle speedup to 10 kph Type of vehicle (vehicle weight range) Brake HydraulicPressure Range Sedan (up to 5,000 lbs.) up to 25 bar Crossover (up to7,000 lbs.) up to 30 bar SUV (up to 8,000 lbs) up to 40 bar* Light DutyTrucks (up to 8,000 lbs.) up to 70 bar* *Although the weight ranges ofSUVs and light duty trucks are similar, the given hydraulic pressurerange of light duty trucks takes into account the higher loadingcapacity and thus higher GVW of light duty trucks compared to SUVs.

In one embodiment, the hydraulic brake pressure at which minisparedetection is suspended varies from 1-70 bar (e.g., for high-p surfaces)to 1-100 bar (e.g., for low-p surfaces). In other embodiments, minisparedetection may be suspended at hydraulic brake pressures above 5 bar, 10bar, 15 bar, 20 bar, 30 bar, 40 bar, 50 bar, 75 bar, or 100 bar.

In various embodiments, the hydraulic pressure within the brake systemis measured at various points in the hydraulic braking system, such asthe master cylinder, at one or more wheels (e.g., using a pressuresensor in the brake caliper), or along the brake lines.

FIG. 2 shows an example system for implementing methods of determiningthe presence of a minispare. FIG. 2 illustrates a vehicle, highlightingthe vehicle's braking system 100 which includes an ABS control system200. The braking system 100 includes a brake pedal 110 coupled to amaster cylinder 120 via a power booster 125, rotors 130 and calipers 140on the front wheels 150, drum brakes 160 on the rear wheels 150,hydraulic brake lines 170 connecting the drum brakes 160 and calipers140 to the master cylinder 120 via an ABS hydraulic unit 210, and acable-operated parking brake mechanism 180 attached to the drum brakes160 on the rear wheels 150. The ABS system 200 includes an ABScontroller 220, the ABS hydraulic unit 210, ABS speed sensors 230 oneach wheel 150 to determine the rotational velocity, the speed sensors230 coupled to the controller 220 via ABS system wiring 235, and atleast one hydraulic pressure sensor 240. The braking system 100 and theABS hydraulic unit 210 are operatively connected together usinghydraulic fluid which flows through the hydraulic fluid lines 170running between the respective components. The hydraulic pressure sensor240 may be incorporated in the master cylinder 120 as depicted in FIG.2. Alternatively, hydraulic pressure sensors 240 may instead or inaddition be incorporated into the brake lines 170, the brake calipers140, or the drum brake 160 assembly.

In operation the ABS system 200 measures the rotational velocity of eachwheel 150 to check for the presence of a minispare tire 300 (FIG. 2). Ifthe vehicle's driver depresses the brake pedal 110, this moves the brakepedal 110 and activates the BLS. There is generally an initial braking‘dead band’ in which the brake pedal 110 moves a short distance beforehydraulic pressure in the braking system 100 begins to increase. As thebrake pedal 100 is pressed further, hydraulic pressure builds in thebraking system 100, which can be measured by the hydraulic pressuresensor 240 in the master cylinder 120 or elsewhere in the hydraulicbraking system 100, e.g. in the calipers 140, drum brakes 160, or brakelines 170. When the hydraulic pressure reaches a certain minimum level,the braking mechanisms (the calipers or shoes) will begin to activateand eventually engage the moving parts (the discs or drums). When thehydraulic pressure reaches a predetermined critical level, theelectronic ABS controller 220 suspends minispare detection until thehydraulic pressure decreases below the critical level. In variousconstructions, suspending minispare detection may involve the controllernot collecting wheel speed sensor information or may involve notaltering the adjustments in the system for the presence of a minisparetire until the brake hydraulic pressure level decreases below thecritical level.

The present methods can be implemented in a like manner with othercontrol systems, such as a TCS or ESC system.

Even for those drivers who use a single foot to control the acceleratorand brake pedals, embodiments of the invention allow for continueddetection for the presence of a minispare tire during light braking. Anadditional feature of one or more embodiments is that the occurrence offalsely setting the wheel speed sensor plausibility fault in thepresence of an installed minispare is reduced.

Various features and embodiments of the invention are set forth in thefollowing claims.

1. A method for detecting a minispare tire in a vehicle, comprising:monitoring a vehicle speed while the vehicle is in motion; monitoring aposition of a throttle of the vehicle; measuring a hydraulic pressure ina braking system of the vehicle during braking; identifying a thresholdhydraulic pressure in the braking system when the vehicle speed deceasesdue to braking while the throttle is applied; and suspending detectionfor the minispare tire when the hydraulic pressure in the braking systemis above the threshold hydraulic pressure during braking while thevehicle is in motion.
 2. The method of claim 1, further comprisingrecording the threshold hydraulic pressure associated with the vehiclespeed and the throttle position in a data storage unit of the vehicle.3. The method of claim 1, further comprising maintaining a constantthrottle position in the vehicle.
 4. The method of claim 1, whereinperforming detection for a minispare tire comprises detecting arotational velocity of each of a plurality of wheels of the vehicle; anddetermining whether a minispare tire is mounted on the vehicle based onthe rotational velocities detected at each of the plurality of wheels.5. The method of claim 1, wherein the threshold hydraulic pressure isequal to the hydraulic pressure measured when the vehicle speeddecreases by 5 kph.
 6. The method of claim 1, wherein the thresholdhydraulic pressure is equal to the hydraulic pressure measured when thevehicle speed decreases by 10 kph.
 7. The method of claim 1, wherein thevehicle comprises a vehicle control system.
 8. The method of claim 7,wherein the vehicle control system is an antilock braking system, atraction control system, or an electronic stability control system. 9.The method of claim 1, wherein the measuring the hydraulic pressure inthe braking system occurs at a master cylinder of the braking system.10. The method of claim 1, wherein the measuring the hydraulic pressurein the braking system occurs at one or more of a plurality of wheels ofthe vehicle.
 11. The method of claim 1, wherein the threshold hydraulicpressure is at least 10 bar.
 12. The method of claim 1, wherein thethreshold hydraulic pressure is at least 25 bar.
 13. The method of claim1, wherein the threshold hydraulic pressure is at least 50 bar.
 14. Themethod of claim 1, wherein the threshold hydraulic pressure is at least70 bar.
 15. The method of claim 1, wherein the threshold hydraulicpressure is at least 100 bar.